Finding a geocache

Puzzle caches are a great alternative to traditional geocache. But for many geocachers, they are too difficult or require too much effort.

This page has been written to give you some tips on how to solve those puzzle caches that might currently be beyond your reach.

It covers what to look for when solving a puzzle cache, some of the clever techniques used to hide clues and how to confirm you're on the right track.

This session was originally presented at the Geocaching NSW 2010 AGM event by founding president, Darren Osborne.

1. Look for patterns

A puzzle cache will typically require you to solve all the digits in the coordinates (15 in total), the minutes (10) or the decimal minutes (6). For example;

AB CD.EFG HIJ KL.MNO - 15 digits

S33 AB.CDE E151 FG.HIJ - 10 digits

S33 26.ABC E151 04.DEF - 6 digits

Solving a 15-digit puzzle is easiest as you can use the degrees part of the coordinates to confirm you're on the right track (see next tip). Puzzles that require 10 digits are typically the hardest.

Armed with this knowledge, you should look at the puzzle to see if there are 6, 10 or 15 objects, items, words, phrases, lines, etc. in the cache description. This may be where the answer is hidden.

2. Study the 'fake' coordinates

Since mid-2008, puzzle caches require the starting, or fake, coordinates to be within about 3.2 kilometres from the actual geocache. In southern Australia, this equates to roughly ±2' (minutes) east/west and ±1.7' north/south. Typically this will also mean the degrees portion of GZ will be identical to the fake coordinates - unless it is close to a longitude/latitude line, which will narrow down your search for 10- and 15-digit puzzles.

For example, if the fake coordinates are S33 24.509 E151 02.677 and you need to solve AB CD.EFG HIJ KL.MNO, you can reduce this to S33 2D.EFG E151 0L.MNO and that D is 3,4,5 or 6 and L is likely to be 0, 1, 2, 3 or 4.

If the puzzle uses repetition – such as AB BB.ACA – this will help you even further.

Example:

The geocache’s starting coordinates are S 33° 46.800 E 151° 01.000

The puzzle asks use to find the cache with the following: AA° BC.DEF GHG° FG.ACG

We could quickly solve most of this as we know A=3, B=4, G=1, H=5 and F=0.

So now our puzzle have been reduced to this 33° 4C.DE0 151° 01.3C1

3. Substitutions

There are many ways to convert numbers and text into something that looks unintelligible.

Below are some examples. To crack the substitution code, look for repetitions and patterns (see tip).

Not all puzzles will solve as numbers. Some spell out the coordinates as words, such as 'south three three ...' or 'south thirty-three', or provide other clues – ‘next to the trig point’.

Ciphers have been used to hide text for thousands of years. In fact the hints that are typically shown on geocache listing pages use the ROT 13 or Caesar shift-13 cipher. ROT5 is a simple numeric substitution cipher. Other substitution ciphers include: substitution, Keyed Caesar, and Pigpen or Masonic. These are all "monoalphabetic" ciphers, meaning that each incidence of any particular letter or number in the original message always encodes to the same symbol in the encrypted message.

ROT13 cipher

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Caesar shift-5

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ROT5

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Keyed Caesar

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Pigpen cipher

The first step to solving these ciphers is to use a technique known as frequency analysis. This involves looking at which letters, or combinations of letters, appear most frequently. For example, the letter E is the most commonly used letter in the English alphabet. If the letter J appears most often in the ciphered text, then you maybe able to assume that J represents E and the cipher could be a Caesar shift-5.

Also look for common combinations that look like THE, THREE, and AND. Other patterns include

The two Es in the word THREE

TY on the end of TWENTY, THIRTY FORTY etc.

SEVEN and SEVENTY repeats E in the 2nd and 4th positions

NINETEEN repeats one character in the 1st, 3rd and 8th places and another in the 4th, 6th and 7th places.

COORDINATES is a relatively long 11 letter word that shows up surprisingly often in geocache ciphers and it has O repeated in the 2nd and 3rd positions so it can be easy to spot.

The topic of ciphers and codes fills volumes of textbooks; far more than we can even begin to outline here. But if you're interested in learning more, here are some related terms worth researching:

Affine

Columnar Transposition

Playfair

Atbash

Double Transposition

Polybius Square

Base64

Enigma

Railfence

Baudot

Keyed Caesar

ROT47

Bifid

Letter Frequency

Steganography

Caesar

One Time Pad

Vigenere

Also, at the end of this article is a list of useful websites.

5. Other coordinate systems

Some puzzles result in coordinates that are not in the commonly used 'degrees-decimal minutes' format. They may be decimal degrees (S33.5684 E151.1789), degrees minutes seconds (S33 24' 31'' E151 03' 12''), or other grid references (UTM55 12 1235).

6. Picture speaks a thousand words

There is more to a picture than the picture itself. Some contain 'hidden' information known as EXIF data. Look at the file’s properties or use a photo editing program to look at the data included with the image to see if there is anything hidden.

Changing various attributes such as brightness, contrast, alpha channel or colour depth may also reveal information.

Try inverting images, or using filters such as ‘Local Equalization’ and ‘Find Edges’ if available. If you don’t have Photoshop, you may find these free software titles useful:

Some puzzle geocaches have clues hidden in the HTML code of the page, also known as the source code. To look at the HTML code, right-click on the page and choose View source. It may be text that is commented out, made white or hidden using some other method.

Because most of the code is generated by the cache listing website, you will only need to look in the section that contains the cache description.

Example:

<span id="ctl00_ContentBody_LongDescription">The 'City gates' caches sit close to large monuments declaring your entry (or exit) of the Australian Capital Territory. But not every border crossing has such an announcement. The border itself is even subtler. <!-- The cache is at S 35° 11.480 E 149° 00.474 --> This line is a comment that won't display on the listing. <p color=white>You won’t see this clue either: It will appear as a blank line. It’s up in the tree.</p> <p>To find the cache you must crack the puzzle. But where is it?</p> <p>There are two ways of getting to this location, both short enjoyable walks - down on the border.<br /></p></span>

8. Confirm your answer

Once you have what you think is the answer, copy and paste it into a mapping program such as OziExplorer, Mapsource or Google Maps (maps.google.com.au). This will give you a first look at whether you have the right answer. If the arrow points to a solitary tree, a gazebo, clump of rocks, fork in the road, etc., you can feel reasonably confident that you have the correct answer. If it lands in the middle of a busy intersection or out in the Pacific Ocean, you probably have more work to do.

Some geocache listing pages include a coordinate checker for you to confirm your coordinates. Some have a ten-minute delay between ‘searches’ or limit the number of searches you can do in any ten minutes, so it’s recommended you try the map test first.

9. Brute force

The final method is to search for the geocache without solving the puzzle - known as brute force. Look at a map of the area to identify any logical hiding places within a reasonable distance of the starting coordinates. Read through the logs and closely examine any photos.

Try searching the internet for the GC code and title for clues. If the description includes what looks like phrases or poetry, search for it on the web - it may provide clues to the author or some other pieces of information.

Whatever technique you use, if you find the cache through this method DO NOT mention it in your log. Some puzzle cache owners may feel cheated and decide to delete your log. It may also encourage other future hiders to follow the same path. Remember, the purpose of the puzzle is for people to solve it, not cheat.

10. Ask for help

When all else fails, email the cache owner (or a previous finder) and ask for a hint. Many are keen to see find logs appear in their email inbox, so they are willing to give you a clue or two.

Like with brute force, if you ask a previous finder for help, it is best not to make mention of this in your log as it may upset the hider. Keep it as your ‘little secret’.